Field of the Invention
The invention lies in the field of printing. The invention relates to an apparatus for printing, in particular, a franking and/or a addressing machine, with a printing head that is held displaceably on a printing-head mounting. In order to achieve the relative movement between the printing head and the medium to be printed, the mounting is configured to be movable, during printing, between a first longitudinal position and a second longitudinal position in a first direction with respect to a base element. Also provided is a first offsetting device that allows the printing of printing images offset to one another transversely to the first direction. The offsetting device is configured for offsetting the printing head relative to the printing-head mounting from a first transverse position into at least one second transverse position spaced from the first transverse position transversely to the first direction. In order to hold the printing head in the first or the second transverse position during printing, a holder for holding the printing head in the respective position is provided.
Within the meaning of the invention, the term xe2x80x9cprinting headxe2x80x9d refers to all types of printing devices that can generate a printing image on a medium. In other words, the term, on one hand, includes printing devices employing any desired printing techniques. Nor is it to be restricted to the component that directly generates the printing image, but may additionally embrace further components that are required for generating the printing image. The components may be, for example, ink reservoirs, etc.
A prior art apparatus is disclosed, for example, in European Patent Application EP 0 933 210 A2. In the apparatus described there, the printing head is disposed displaceably in a mounting guided by a guide rod. For printing, the mounting and, therefore, the printing head are moved in a first direction, to be precise, parallel to the guide rod.
When a first printing image has been generated, the printing head is offset relative to the mounting perpendicularly to the first direction, in order, in a further step, to generate a second printing image, with the printing head being moved in the first direction in the opposite sense. The offset of the second printing image to the first printing image is such that the two printing images overlap one another at most in the edge region in which they are contiguous to one another transversely to the first direction. It is, thereby, possible to generate by a printing head an entire printing image of which the dimension transverse to the first direction, that is to say transverse to the printing direction, corresponds approximately to double the printing width of the printing head.
In the prior art apparatus, the offsetting device is disposed on the mounting and is configured as a linear drive that acts on the printing head. Naturally, the linear drive also assumes the function of a holder.
Such a configuration has a disadvantage that the use of the linear drive for holding the printing head in the respective transverse position necessitates a relatively complicated activation of the drive, if appropriate even a position control, in order to ensure exact positioning of the printing head. Moreover, the drive must deliver a particular holding moment in both directions of movement, in order to ensure exact positioning during the printing operation.
It is accordingly an object of the invention to provide an apparatus for guiding a printing head that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that, at low outlay, ensures exact and reliable positioning of the printing head during printing.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an apparatus for printing, including a base element, a printing-head mounting moveably connected to the base element, a printing head displaceably connected to the printing-head mounting, the printing-head mounting configured to move, during printing, between a first longitudinal position and a second longitudinal position in a given direction with respect to the base element to effect a relative movement between the printing head and a medium to be printed, an offsetting device for printing images offset to one another transverse to the given direction, the offsetting device configured to offset the printing head relative to the printing-head mounting from a first transverse position into at least one second transverse position spaced from the first transverse position in a direction transverse to the given direction, and a holder for holding the printing head in at least one of the first transverse position and the second transverse position during printing, the holder having at least one first holding device and at least one second holding device, each of the at least one first holding device and the at least one second holding device having at least one stop for limiting movement of the printing-head transverse to the given direction. Preferably, the printing apparatus is a franking machine.
The invention is based on the technical teaching that a particularly simple apparatus with transverse positioning of the printing head, the transverse positioning conforming well to the accuracy requirements, is obtained when the means for holding the printing head in the respective transverse position has at least one first holding device and one second holding device that respectively include at least one stop for limiting the printing-head movement transversely to the first direction.
In accordance with another feature of the invention, at least one holding device has a stop with a stop surface, and the stop is disposed on the printing-head mounting.
In a refinement according to the invention, it is necessary merely for the relative positions of the stop regions disposed on the printing head and the relative positions of the stops cooperating with these to be within specific predetermined tolerances in order to ensure sufficiently exact positioning.
Contact between the stop regions disposed on the printing head and the stops may, in such a case, be punctiform or linear, but, for reasons of wear, it preferably takes place over an area in order to obtain low local surface pressure during contact.
The stops may be disposed fixedly on the apparatus, for example, on the base element. During the movement of the printing head during printing, the respective stop regions on the printing head then brush over the respective stop cooperating with them. Preferably a stop surface of the stop of at least the first holding device is disposed on the printing-head mounting. One advantage is that such a stop is largely free of wear because, during printing, it does not experience any movement relative to the printing head and, therefore, as a rule, has no appreciable tangential forces acting upon it, but, instead, mainly normal forces. Consequently, it does not undergo any appreciable frictional wear.
In accordance with a further feature of the invention, the there is provided a force member for providing a contact force, and at least one holding device is configured to hold the printing head in at least one of the first and second transverse positions by the contact force acting on the stop.
The first holding device holding the printing head in the corresponding transverse position can ensure the transverse positioning of the printing head during printing by positive connection. In order to ensure reliable positioning of the printing head during printing in a simple way, the first holding device is configured preferably for holding the printing head in the associated transverse position by a first contact force acting on the stop.
For such a purpose, in preferred variants of the apparatus according to the invention, a spring device for achieving the first contact force by spring action is provided. The spring device can act directly on the printing head and prestress the printing head against the stop. The prestress and, therefore, the contact force are selected such that the respective stop region of the printing head is constantly pressed against the associated stop during the printing operation.
In further variants, a magnetic device may be provided for achieving the first contact force by magnetic action. A magnet may be provided on the printing head, which, in order to generate the contact force, cooperates with a further magnet or an element of magnetic material, for example, iron or the like, which is disposed preferably in the region of the stop. Alternatively, a corresponding element of magnetic material may also be provided on the printing head, which, in order to generate the contact force, then cooperates with a magnet preferably disposed in the region of the stop.
In accordance with an added feature of the invention, the first holding device is configured to hold the printing head in the associated transverse position by a first locking element acting by positive connection. Then, it is not necessary for the printing head to be prestressed against the respective stop when the locking element acts positively in both directions transversely to the first direction, insofar as the positive connection has sufficiently small play.
It goes without saying that the locking element may also act positively in one direction only, that is to say, forms the stop or the stop region, cooperating with the stop, on the printing head. Then, in order to position the printing head, a corresponding contact force on the stop must also be established in the way described.
Preferably, the first holding device is configured to automatically lock the first locking element when the associated transverse position is reached. At the same time, also preferably, the actuation of the locking element takes place by the movement of the printing-head mounting and, therefore, of the printing head in the first direction. For such a purpose, the locking element may be configured, for example, as a correspondingly shaped lever that is prestressed by spring action and that is actuated, during the movement of the printing-head mounting, by running onto corresponding control elements, for example, simple ramps or the like, for locking or releasing the lock.
The second holding device may be configured in a similar way in the manner of the first holding device. The variants mentioned may, however, also be combined with one another in any desired way.
Simply constructed and, therefore, advantageous developments of the apparatus according to the invention are distinguished in that at least the second holding device includes a first longitudinal guide device and a second longitudinal guide device cooperating with the latter. The second longitudinal guide device cooperates with the first longitudinal guide device such that the printing head is guided essentially parallel to the first direction. Furthermore, at the same time, one of the two longitudinal guide devices is disposed on the base element. A simple configuration is, therefore, implemented that reliably ensures transverse positioning.
The term xe2x80x9clongitudinal guide devicexe2x80x9d within the meaning of the invention embraces any desired device(s) that, when cooperating with a counterpart, influences the direction of the relative movement between the longitudinal guide device and the counterpart.
In favorable developments of the apparatus according to the invention, the first longitudinal guide device has at least one first longitudinal guide surface essentially parallel to the first direction. The second longitudinal guide device is formed by a longitudinal guide element that cooperates with the first longitudinal guide surface in order to hold the printing head in the respective transverse position.
In such a case, during the cooperation of the longitudinal guide devices, the longitudinal guide element brushes over the first longitudinal guide surface. The longitudinal guide element may have a second longitudinal guide surface over which the active partner brushes during the cooperation of the longitudinal guide devices. It is likewise possible, however, for the longitudinal guide element to be configured such that linear or punctiform contact with the first longitudinal guide surface occurs.
As long as contact, that is to say, the action of a contact force, is ensured between the two longitudinal guide devices, a defined movement of the printing head during offsetting is also guaranteed. The contact force may be ensured, for example, by a spring that acts on the printing head.
Preferably, the first longitudinal guide device is formed by a longitudinal guide groove and the second longitudinal guide device is formed by a longitudinal guide pin, thus, resulting in a configuration that is particularly simple to produce and has reliable guidance. Moreover, such a configuration ensures positive guidance, which allows reliable guidance even without any separate prestressing of the two longitudinal guide devices against one another.
In accordance with a concomitant feature of the invention, the longitudinal guide device disposed on the base element extends at least in the region between the first and the second position of the printing-head mounting to ensure, in a simple way, reliable transverse position of the printing head during the printing operation between the first and the second position of the printing-head mounting.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an apparatus for guiding a printing head, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.